1. Field of the Invention
This invention relates to an imaging method based upon the chemical reactivity of a select pair of photoactive materials. More specifically, this invention concerns itself with a method for image creation based upon the photoinduced oxidative or reductive degradation of one of the above select materials. Dispersal of these materials in a polymeric film and the subsequent selective photoinduced decomposition of one of said materials will induce certain changes within the polymeric film thereby altering the films optical and/or physiochemical properties in those regions corresponding to such decomposition.
2. Description of the Prior Art
The use of organic compounds as photosensitive medium for photographic processes is well known and is perhaps best exemplified by the diazo process. This process is based upon the photochemical changes effected in various diazonium salts upon exposure to activating energy thereby altering the capacity of such salts to form dyes. In general, dyes are formed when such diazonium compounds or a diazotized amine couple with phenols or aromatic amines in an alkaline medium. Upon exposure to light, diazonium compounds undergo decomposition and are thus rendered incapable of coupling and thereby dye formation is precluded. This type of photolytic degradation of diazonium compounds is commonly employed in copying papers. For example, in one such copy paper based process, a diazo anhydride and a coupler are dispersed in a neutral medium, the paper exposed to activating energy of the appropriate wavelength and thereafter developed by contacting with ammonia fumes. In another analogous process, the paper which is coated with a diazo compound is developed by immersion in alkaline solution containing the dye coupler.
The photolytic degradation products of diazonium compounds can also be used as reducing agents in the conversion of the leuco form of certain phthalocyanine compounds to higherly colored materials, see U.S. Pat. No. 2,884,326. In this system, the leuco form of phthalocyanine and a diazonium compound are dispersed in a water permeable colloid and the resultant dispersion coated as a film on a supportive substrate. After this film has dried, it is exposed to activating electromagnetic radiation and thereafter the film is treated with a solvent capable of dissolving the leuco form of phthalocyanine compounds. Alternatively, the exposed film can be treated with a solution of strong acid. In either event, a positive image is produced within the coating by conversion of the leuco form of phthalocyanine to its highly colored counterpart.
In each of the systems described hereinabove, image formation is based upon the selective decomposition of a diazonium compound either to render it incapable of coupling with other materials or to assist in conversion of a colorless compound to its highly colored counterpart.
Photolytic degradation processes have also been used in the preparation of relief images from certain photodegradeable polymers, see for example, U.S. Pat. No. 3,558,311; and 2,892,712 (examples VII and IX). In the above patented processes, selective illumination of an imaging layer containing a degradeable polymer results in its degradation into lower molecular weight material. The products of such degradation differ from the non-degraded polymer and thereby provides a basis for image formation. In the 3,558,311 patent, the selective illumination of a polymer containing an oxime ester results in the degradation of this material in the exposed regions of the film wherein this ester is present. The image is "developed" by removal of the degraded material from the imaging layer with solvents which are specific for the degradation products but non-solvents for the materials in the exposed regions of the imaging layer. The '711 patent is similar in its disclosure, however, subsequent to imaging of the film, the light destabilized formaldahyde polymer is "developed thermally". In both of the polymer based imaging systems referred to hereinabove, the intensity and duration of exposure required to produce photolytic degradation within such films is quite extensive. Moreover, even after such intensive exposure to imaging energies, the image is still not visible, but requires additional development either with solvents or by thermal treatment. These systems are, thus, inefficient, expensive and generally impractical for commercial use.
Recently a number of patents have issued which reportedly enhance the selective degradation of polymers, such as poly(acetaldehyde). Such enhancement in degradation is achieved through the combination of the poly(acetaldehyde) with a variety of other materials; such as polymers capable of undergoing dehydrohalogenation and/or a variety of sensitizer materials which are photoactivated and thereby initiate breakdown of the degradable polymer. These patents are as follows: U.S. Pat. Nos. 3,915,704; 3,915,706; 3,917,483; 3,930,858; 3,951,658; 3,963,491; and 3,964,707.
Notwithstanding the advances made in the art which are reported in the above patents, further refinement is still required; especially in adapting these improved systems for use with both visible light and laser input. In the absence of compatibility of the above prior art systems with laser input, it is not as yet possible to prepare high resolution vesicular images from direct irradiation with highly colliminated light without additional development and/or intensification of the latent image with thermal energy.
Accordingly, it is the object of this invention to remedy the above as well as related efficiencies in the prior art.
More specifically, it is the object of this invention to provide an imaging method utilizing the chemical reactivity of photoexcited states of certain select materials.
Another object of this invention is to provide an imaging method wherein image creation is based upon photoactivation of either component of the pair of select materials thereby resulting in the decomposition of the less chemically stable component of the pair of select materials.
Additional objects of this invention include the preparation and use of imaging members based upon the above photoactive chemical decomposition processes.